Abstract
Employing two-dimensional molecular dynamics (MD) simulations of soft particles, we study their non-affine responses to quasi-static isotropic compression where the effects of microscopic friction between the particles in contact and particle size distributions are examined. To quantify complicated restructuring of force-chain networks under isotropic compression, we introduce the conditional probability distributions (CPDs) of particle overlaps such that a master equation for distribution of overlaps in the soft particle packings can be constructed. From our MD simulations, we observe that the CPDs are well described by q-Gaussian distributions, where we find that the correlation for the evolution of particle overlaps is suppressed by microscopic friction, while it significantly increases with the increase of poly-dispersity.
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Notes
The number of particles and size ratios of poly-dispersed particles are resembling the recent experiments of wooden cylinders [8].
We confirmed that static packings prepared with longer length scales, \(\lambda =10^3\bar{\sigma }\) and \(10^4\bar{\sigma }\), give the same results concerning their critical scaling near jamming [10], while we cannot obtain the same results with a shorter length scale, \(\lambda =10\bar{\sigma }\).
Here, \(p/k_\mathrm {n}\) is dimensionless in two dimensions and the scaled distances for radial distribution functions, g(r), are defined as \(r\equiv d_{ij}/(R_i+R_j)\).
Because every acceleration is lower than the threshold, the viscous forces are negligible, while they play an important role during the relaxation process.
Such a discontinuity is specific to static packings, where a corresponding gap has been observed in a radial distribution function in a glass with zero-temperature [12].
From the Chapman–Kolmogorov equation (9), \(P_{\phi +\delta \phi }(\xi ') = \int _{-\infty }^\infty \delta (\xi '-\xi ^\mathrm {affine})P_\phi (\xi )\mathrm{d}\xi = \int _{-\infty }^\infty \delta (\xi '-B_a\gamma -\xi )P_\phi (\xi )\mathrm{d}\xi = P_\phi (\xi '-B_a\gamma )\).
B(x, y) is the beta function.
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Acknowledgments
We thank M. Tolomeo, V. Richefeu, G. Combe, and G. Viggiani for fruitful discussions. This work was financially supported by the NWO-STW VICI Grant 10828, the World Premier International Research Center Initiative (WPI), Ministry of Education, Culture, Sports, Science, and Technology, Japan (MEXT), and Kawai Foundation for Sound Technology & Music. This work was also supported by Grant-in-Aid for Scientific Research B (Grants Nos. 16H04025 and 26310205) and Grant-in-Aid for Research Activity Start-up (Grant No. 16H06628) from the Japan Society for the Promotion of Science (JSPS). A part of numerical computation has been carried out at the Yukawa Institute Computer Facility, Kyoto, Japan.
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Saitoh, K., Magnanimo, V. & Luding, S. The effect of microscopic friction and size distributions on conditional probability distributions in soft particle packings. Comp. Part. Mech. 4, 409–417 (2017). https://doi.org/10.1007/s40571-016-0138-z
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DOI: https://doi.org/10.1007/s40571-016-0138-z